Used WTW Oximeter, model 330i.
Beautiful handheld pocket of WTW oxygen meter, including CellOx 325 sensor (probe), comes with case as shown on the photos.
Technical specifications:
Powered by batteries, 4x 1.5V AA.
Type of protection: IP 66
Dimensions Oxi meter (W) x (D) x (H): 9 x 18 x 5 cm.